Automated data storage libraries are known for providing cost effective storage and retrieval of large quantities of-data. The data in automated data storage libraries is stored on data storage media that are, in turn, stored on storage shelves or the like inside the library in a fashion that renders the media, and its resident data, accessible for physical retrieval. Such media is commonly termed “removable media.” Data storage media may comprise any type of media on which data may be stored and which may serve as removable media, including but not limited to magnetic media (such as magnetic tape or disks), optical media (such as optical tape or disks), electronic media (such as PROM, EEPROM, flash PROM, Compactflash™, Smartmedia™, Memory Stick™, etc.), or other suitable media. Typically, the data stored in automated data storage libraries is resident on data storage media that is contained within a cartridge and referred to as a data storage media cartridge. An example of a data storage media cartridge that is widely employed in automated data storage libraries for mass data storage is a magnetic tape cartridge.
In addition to data storage media, automated data storage libraries typically contain data storage drives that store data to, and/or retrieve data from, the data storage media. The transport of data storage media between data storage shelves and data storage drives is typically accomplished by one or more robot accessors (hereinafter termed “accessors”). Such accessors have grippers for physically retrieving the selected data storage media from the storage shelves within the automated data storage library and transport such media to the data storage drives by moving in the X and Y directions. As such, it is important that accessors have the capability of being able to accurately locate storage shelves and data storage drives.
Fiducial (calibration) targets are provided within a library to align the storage shelves and data storage drives with the accessor. There is often difficulty in debugging field problems when a fiducial target cannot be found at an expected location in the library. These types of errors can be caused by a variety of reasons, including firmware or mechanical causes. As an example, if the accessor is searching for a fiducial target with its calibration sensor and cannot find it in the expected location, then the library calibration process will fail. When debugging this event from logged library event data, it doesn't provide a picture of where the calibration sensor was searching relative to the physical location of the fiducial target. All that is known is the absolute location at which the sensor was searching.
One solution to this problem would be to have a camera that would take a picture of the area in question. However, drawbacks to this solution are that it adds additional cost related to the incorporation of the camera into the accessor, requires additional firmware and hardware be added to the accessor, requires additional processor and network bandwidth in operation, and has a limited availability on existing library systems. The challenge therefore is to provide a better solution in handling library calibration errors that result in a fiducial target not being in an expected location.